Magnetically coupled valves are well known devices for use in systems in which fugitive emissions cannot be tolerated. One such valve is taught in Canadian Patent No. 1,092,589 issued on Dec. 30, 1980 to Nova Scotia Research Foundation Corporation. That valve is a rotary valve and has its valve member, e.g. a butterfly, attached to a valve stem which is rotatable on a rotation axis and which is also attached to a carrier. The carrier mounts a plurality of rare earth magnets about its outer periphery, with adjacent magnets having alternate polarity. The carrier is enclosed by a barrier member which is hermetically sealed to the valve body so that hazardous material passing through the valve is always contained within the barrier member and the valve body.
Externally of the barrier member is another carrier, usually annular in shape, this carrier mounting another plurality of rare earth drive magnets about the internal circumference thereof, these magnets also being of alternating opposite polarity. A suitable means, such as a handle, valve actuator, or lever arm, is provided to effect rotary movement of the drive carrier relative to the stationary barrier. Magnetic interaction across the barrier member causes the internal driven carrier to follow the rotary movement of the external drive carrier so that the valve member is rotated to progressively open or close tile valve. Rotation limit means can be provided to prevent the valve member from rotating too far in the valve body.
Linear magnetic valves are also available, operating on essentially the same principles. The valve member is adapted to reciprocate between limits corresponding to completely open and completely closed conditions of the valve. The valve member is connected to a valve stem which is also connected to a carrier. The carrier mounts a plurality of rare earth magnets about its outer periphery, with adjacent magnets being of alternating polarity. The carrier and the valve stem are enclosed by a barrier which is hermetically sealed to the valve body so that hazardous material passing through the valve is always contained within the barrier member and the valve body.
Externally of the barrier member is another carrier, usually annular in shape, this carrier mounting a plurality of rare earth drive magnets about the internal circumference thereof, these magnets also being of alternating opposite polarity. A suitable means such a pneumatic motor connected to a yoke is provided to effect reciprocating movement to the drive carrier relative to the stationary barrier. Magnetic interaction across the barrier member causes the internal driven carrier to follow the linear movement of the external drive carrier so that the valve member is moved to progressively open or close the valve.
There may be instances in which either type of valve, capable of handling heavy flow volumes, will jam and the drive forces available magnetically may not be sufficient to overcome the jam. It is therefore imperative that there be some mechanism available to override the magnetic operation of the valve so that the valve can be either opened or closed by hand until such time as the fault which caused the jam can be rectified. Usually the fault is such that the valve must be dismantled, repaired, and rebuilt; otherwise there would have been no problem in the first place.